The kidneys are a pair of organs that lie in the back of the abdomen on each side of the vertebral column. Kidneys play an important regulatory role in maintaining the homeostatic balance of the body. The kidneys function like a complex chemical plant. The kidneys eliminate foreign chemicals from the body, regulate inorganic substances and the extracellular fluid, and function as endocrine glands, secreting hormonal substances like renin and erythropoietin.
The main functions of the kidney are to maintain the water balance of the body and control metabolic homeostasis. Healthy kidneys regulate the amount of fluid in the body by making the urine more or less concentrated, thus either reabsorbing or excreting more fluid, respectively.
In case of renal disease, some normal and important physiological functions become detrimental to the patient's health. This process is called overcompensation. In the case of Chronic Renal Failure (CRF) patients overcompensation often manifests in hypertension (pathologically high blood pressure) that is damaging to heart and blood vessels and can result in a stroke or death.
The functions of the kidney can be summarized under three broad categories: a) filtering blood and excreting waste products generated by the body's metabolism; b) regulating salt, water, electrolyte and acid-base balance; and c) secreting hormones to maintain vital organ blood flow. Without properly functioning kidneys, a patient will suffer water retention, reduced urine flow and an accumulation of wastes toxins in the blood and body.
The kidney is made up of about a million tiny units called nephrons. The nephron is where blood carrying capillaries intertwine with tiny waste-processing tubules. A complicated chemical exchange takes place in the nephron where waste materials and water leave the blood via the capillaries and enter the urinary system via the tubules. Every day a person's kidneys sift out about 2 quarts of waste products and excess water from the blood. On average the kidneys process about 200 quarts of blood. The waste and extra water become urine, which typically flows through the ureters to the bladder.
Extreme trauma may result in the loss of kidney function. This loss of function results in the retention of excess fluids within the kidneys and the build up of waste products, such as nitrogen. When the kidneys stop working over a period of hours, days, or weeks renal failure results. The most common causes of acute forms of renal failure include dehydration, direct trauma to the kidneys, decreased cardiac output, blood loss, and various medications; such as contrast agents used in X-ray tests, nonsteroidal anti-inflammatory drugs (NSAIDs), and antibiotics. During renal failure excess fluids are not removed by the kidneys and the body's normal chemical balance is upset as chemicals and electrolytes, such as sodium, potassium, and calcium, build up to abnormally high levels and become toxic to the body.